For every gallon of biodiesel produced, one pound of glycerin also obtained as a side-product. Biodiesel production is expected to produce an additional one billion pounds of glycerin per year due to the expanding number of plants. Also, about 557 million pounds of glycerin was produced from non-biodiesel sources in 2003. Although there are currently some markets for glycerin, there is mounting concern that glycerin prices may plummet to 5-10 cents per pound or less if future production exceeds demand. Developing a system to make high value chemicals from the glycerin stream will add value for biodiesel producers and maintain a reasonable glycerin price.
The diol, 1,3-propandiol (“PDO”), is currently produced mainly from fossil-based resources by costly chemical processes. The market for PDO is currently about 100 million pounds per year and is growing very rapidly. PDO can be used to prepare new classes of polymers with enhanced functionality. For example, both DuPont and Shell Chemicals have announced plans to commercialize a new polyester, polytrimethylene terephthalate (PTT), wherein PDO has been substituted for ethylene glycol in polyesters. 1,3-Propanediol is a key component of PTT fibers. These fibers display outstanding mechanical and chemical resistance, which are the best characteristics of nylon and polyester.
For example, 1,3-propandiol is a valuable monomer used in industrial polymer syntheses. Traditionally, reduction of polyols can be achieved by either homogeneous hydride reagents or by enzymes. Hydrides, such as lithium aluminum hydride or sodium borohydride, can be explosive and are typically sensitive to moisture. Also, selective reduction of polyols can require multiple protection and deprotection steps due to the presence of multiple hydroxyl groups. These transformations extend and complicate the synthetic procedure. Moreover, each selective protection and deprotection step on a polyol is a challenging task. On the other hand, even through enzymes in general provide high selectivity for chemical reactions, producing large quantities of the target product requires specialized reactors, laborious processes, and specialized enzymes.
Other methods to produce PDO involve fermentation (see Bock et al. “Bioconversion of Glycerine to 1,3-Propanediol as Alternative Use of a By-Product.” Freiberger Forschungshefte A 2002, A866, 125-132; Zeng and Biebl; “Bulk Chemicals From Biotechnology The Case of 1,3-Propane-Diol Production and the New Trends”; Biochemical Engineering Division, GBF—German Research Centre for Biotechnology, Braunschweig, Germany. Advances in Biochemical Engineering/Biotechnology 2002, 74 (Tools and Applications of Biochemical Engineering Science), 239-259; Zeng et al. “Microbial Conversion of Glycerol to 1,3-Propanediol: Recent Progress”; ACS Symposium Series 1997, 666 (Fuels and Chemicals from Biomass), 264-279; and Wang et al.; “Conversion of Glycerol to 1,3-Propanediol via Selective Dehydroxylation” Industrial & Engineering Chem. Res. (2003), 42(13), 2913-2923), hydrogenolysis (WO 99/05085 (Drent et al.; “Hydrogenolysis of Gycerol”)), and hydrogenation (Schlaf et al., “Metal-Catalyzed Selective Deoxygenation of Diols to Alcohols”; Angew. Chemie, 2001, 40, 3887-3890)). The hydrogenation method of Schlaf generated both PDO and 1-propanol. Dennis Miller and coworkers (WO 03/035582 (Werpy et al.; “Hydrogenolysis of 6-Carbon Sugars and Other Organic Compounds”)) have evaluated the conversion of glucose and glycerin into 1,2-propanediol. Their high temperature organometallic methodology uses hydrogen gas as the hydrogen atom source. Each of these methods have significant drawbacks, including high costs, cumbersome nature, inefficiency, and the use of various toxic processes and reagents.
Accordingly, there is a need for alternative methods to prepare 1,3-propanediol. These alternative methods would preferably be environmentally friendly, economical, efficient, and easy to perform. The development of new, cost-competitive processes that utilize renewable feedstocks to produce PDO would be an important advance. Introduction of such processes would avoid the use of petroleum, provide substantial energy savings (10 to 19 trillion BTU), and afford a significant market for the bio-products industry.